Process of producing ketene



Feb. 22, 1938. J. slxT ET AL I PROCESS OF PRODUCING KETENE MMM.

'25 vented to a great, in fact to a predominant degree, Carborundum pieces coated with sodium meta- 25 40 tent. or by using from the very beginning dilute the end ofthe apparatus-maintained the system 40 45 absorption, or it is obtained on the pressure side 0f the total anhydride formed, namely 18.5 45

nasal resa-,1938- UNlTED STATES PATENT OFFICE PltooEss or rnonnomo KETENE Johann Sixt and lMartin Mugdan, Munich, (llor-` many, assignors to Consortium fr Elektrochemischc Industrie. G. m. b. H., Munich, Germany, a corporation oi' Germany Appllooaop september s, 1934, serial No. 'Masas In Germany September 16. 1933 9 claims. (ci. zoo-12s) ,This invention relates to a process of producthe ketene to recombine with the excess acetic ing ketene from acetic acid. acid and thereby disappear. It was never thought In the processes disclosed in Meingast 8i possible to obtain ketene as a ilnal product, hence Mugdan Patents No. 1,570,514 of Jan. 19, 1926, no measures have ever been taken with a view to No. 1,636,701 of July 26, 1927, and No. 1,946,707 its isolation or further elaboration. The applica- 5 of Feb. 13, 1934 and other patents, acetic anhytion of such measures, herein described, is essendride is obtained by heating acetic acid vapor to tial for the present process. We have also found temperatures of 40G-800 C., in the presence of that the partial recombination of the ketene with catalysts. The reaction takes place according to water to form acetic acid in the spaces behind the lo the equation: ddl t th u m f H g a ng o e vapors sma quant es o nitrogen- ZCHOOH@ o) 2O+H2O containing bases such as ammonia, pyridine, diy It has been -assumed that the primary product methylamine or trimethylamine. 0f this' Splitting up is not anhydride.,but ketene. The invention is illustrated by the following exwhich is generated according to equation: amples taken in connection with the accompany- 15 cnooooH=CHico+Hio and only then forms `anhydride with acetic acid apparatus for carrying4` out the process. beyond the heating zone, according to the follow- Example I ing formula: thi bo In sem diment of the invention, which is CH2CO+H3COOH (CHQCO) 20 illustrated in Fig. 1, we employed an electrically We have found that the ,ketene primarily heated copper tube 1 measuring 25 mm. in diamformed according to-this assumption can be preeter and 1000 mm. in length, illed with pea size from combining with acetic acid and water to phosphate. One end of the tube was connected form anhydride 0r acetic vafldimd can be iSOlated. to an acetic acid evaporator 2 while the other end by Acarrying out the process of splitting up the was connected to a narrow tube 3 adapted to carry acetic acid under leSS than atmospheric pressure, oil the dissociation products. The tube emptied at between 400-900 C. and by subjectinge the into a Liebig cooler 4 to which a cooled receiver 30 vaporous product of the splitting, which is under or condenser 5 was joined. 'I'his was followed by vacuum, to condensation by cooling under `such a second condenser 6 cooled by means of cooling conditions as to allow the ketene insufficient time brine of minus 50 C. From condenser 6 the gases to combine with the acetic acid or the water. were'passed into two vessels 1 and 8 filled with 'Ihis can be done, for example. by preventing the acetic acid, the vessel 8 being cooled to minus 60 35 condensation from taking place in spaces which C. and containing an addition of acetone in order l are too large, or by passing the split vapors to prevent freezing up. These two latter vessels through a cooled liquid such as water which disserved to `determine the ketene by transformation solves the ketene not at all or only to a small exinto anhydride. A vacuum pump 9 located at acetic acid for the ketene formation. 'I'he ketene under an absolute pressure of about 15 mm. In gas .thus separated under low pressure from the one hour 1055 grams of acetic acid vapor were supacetic anhydride, acetic acid and water is then plied to the tube I at a contact temperature of isolated by cooling to aflow temperature or by 650 C. (measured at the end the contact layer).

of the vacuum pump. 'I'he ketene gas can also grams, 75% was found in receivers 5 and 6 and be transformed into anhydride or other com-A 25% was found inthe two acetic acid receivers pounds by permitting it to react upon water-free 1 and 8, as anhydride. This latter portion corre- `acetic acid.

It has already been proposed to eil'ect the splitdecomposition were negligible.

ting up of acetic acid under reduced pressure but E l H ketene has never been obtained by-that method. ramp e It would seem that the split vapors have always 105 grams oi' acetic acid vapor, containing 0.2% been condensed in apparatus of very large surpyridine vapor, were passed-through the apparaface or under such other conditions as to allow tus described. in Example I, at 650 C. OI the 55 receivers 1 and Example III' The apparatus of Example I was modified to the extent that, instead of the Liebig cooler I and receiver 5, we used a vessel containing 100 grams of water cooled to C., through which the hot split vapor products were passed. 105 grams of concent1-ated acetic acid produced, in one hour at 650 C. contact temperature, a total of 19.0 grams of anhydride, of which 11% was found in receivers and 6, and 89% (as transformation product of the free ketene) was found in receivers land 3.

Erllmple 1V The operation was the same as in Example III except that 1% pyridine was added to the water as a preliminary measure. An aggregate quantity of 55.5 grams anhydride was produced of which 31.6% were obtained in receivers 5 and 6, and 68.4% in receivers 1 and 8.

Example V The operation was performed according to Example III except that the ketene discharged from receivers 5 and 6.was not allowed to react upon acetic acid, but was separated out by means of two low-cooled receivers arranged one behind the other like vessels 1 and 8 of Fig. l and each filled with 100 cubic centimeters of acetone to dissolve out the ketene. With an average of 105 grams of concentrated acetic acid per hour there were formed 20 molecules of anhydride plus ketene to every 100 moleculesof acetic acid vapor, of which 4.4 molecules were found in receivers 5 and 6 as anhydride and 15.6 molecules in receivers 1 and 3 as pure ketene. There were no acetyl losses.

It is also possible to condense the ketene without solvents if thetemperature is maintained sufiiciently low, as, for example, less than -100.

Example VI In this embodiment of the invention, which is illustrated in Fig. 2, we employed a vertical tube I0 composed of carbon, measuring 50 mm. in diameter and 800 mm. in height, stopped at the lower end by a carbon stopper. This vessel was mounted in an iron container II closely surrounding the carbon tube and heated electrically. From the flanged cover of container II a copper tube is led nearly to the bottom of .the carbon tube. The carbon tube I0 was lled to a height of 100 mm. with an equimolecular mixture of sodium metaphosphate and lithium metaphosphate. Two cooled receivers I3 and Il were attached to the iron container II, receiver I3 being cooled with water and receiver Il being cooled with brine at minus 20 C. The gases were then carried up through a dripping tower I5 which was filled with Raschig rings, and sprayed with concentrated acetic acid. The gases passed thenthrough a water filled bottle I6 which re-v tained traces of acetic acid; a vacuum pump I1 was attached to this bottle, whereby an absolute pressure of 30 to 60 mm. of mercury was maintained. The glacial acetic acid was passed through the with 0.3% pyridine vapor with a speed of about 600 grams per hour. Altogether 296 grams of anhydride were obtained from 330 grams of acetic acid which were exposed to the splitting 1,946,707, particularly the use of reaction tube in one hour.

melted catalyst heated to 730 C.

up. Of the anhydride a quantity of 21% was found in the condensates of the two coolers I3 and I4, and 79%l had formed from ketene in the dripping tower I5. The loss in acetyl amounted to 5.5% of the acetic acid used for the splitting processes.

We furthermore found that in carrying out this process the utilization of the gaseous catalysts described in the above mentioned Patent phosphorus, phosphoric acid and volatile esters of phosphoric acid, offers considerable advantages as thereby disturbances through scattering or spraying which may otherwise occur at high gas velocities, are avoided.

Example VII The apparatus of ExampleVI was employed but the carbon tube I0 was empty. At an interior temperature of 700 to 740 400 grams of acetic acid vapor were passed through the Four parts per mil. triethylester of phosphoric acid were added to the acetic acid vapor, as catalyst. At the end of the apparais an absolute pressure of 35 mm. mercury was maintained. 0f anhydride formed, which was 200 grams, 41% was found in the absorption tower as transformation product of ketene` gas, and 59% was found in the cooler condensates.

Example VIII The operation was carried out according to Example VII except that 3 parts pyridine per mil. were added to the acetic acid-triethylphosphate mixture and 300 grams of the mixture were supplied to the heaterin lan hour. 0f the aggregate quantity of 220 grams of anhydride formed, 75% was obtained by absorption of the ketene gas in the dripping tower, and only 25% condensed out The\ of the split vapor products by the cooler. loss amounted to only 4% of the acetic acid employed for the splitting process.

Example' IX The operation was performed according to Example VII except that, instead of triethyphosphate, 0.5 part per mil. of phosphorus vapor Vwas added to the acetic acid vapor. Of the total anhydride obtained, 27% was found in the ketene absorption.

' Example X The operation was performed according to Example VIII except that, instead of ethyl phosphate and pyridine, 1 part per mil. phosphoric acid and 1 part per mil. ammonia were added to the acetic acid vapor. Of the total anhydride obtained, 40% was the result of absorption of ketene.

It was further found that in this process the operation can be carried on with very good results substantially above 800 C. The ketene yield increases without position to any substantial extent. The explanation of this may possibly be found in the short sojourn of the diluted vapors in the hot space and at the hot wall of the reaction chamber.

Example XI An empty heated carbon tube, as in Example VI, without a catalyst charge, was used as the reaction vessel. Also the other disposition was the same as in Example VI. The interior of the tube was maintained at a maximum temperature of 830 C., 600 grams of acetic acid vapor containing 3 parts triethylphosphate per the total quantity of f increasing the decom' while an absolute pressure of 35 mm.V mercury was maintained at the end of the apparatus. An aggregate quantity of 475 grams of anhydride was formed. Of this, 17% was in the cooled condensates and 83% in the liquid iiowing from the ketene absorption acid. 'I'he decomposition loss amounted to only about 3% of the acetic acid used for the splitting process.

Example XII The operation was performed according to Example XI except that instead of the triethylphosphate 0.5 part phosphorus per mil. was supplied to the acetic acid vapor. At a maximum temperature of 870 C. in the interior of the reaction space, from 800 grams of acetic acid vapor which were supplied in one hour, 375 grams of anhydride were obtained, 74% of which was produced through absorption ofthe ketene and 26% of which was found in the condensates. 'I'he decomposition was small.

' Example XIII 'Ihe operation was performed'according to Example XI except that, in addition to the `triethylphosphate, 3 parts pyridine vapor per mil. were added to the acetic acid vapor. At a maximum temperature of 890 C. in the interior of the carbon tube, and with 1160 grams of acetic Small.

In carrying out our invention we may also emhave proven advantageous for the production of anhydride, as, for example, preheating the acetic acid vapor, utilization of other or special catalysts, construction materials and apparatus.

rli'he term vacuum as used ln the claims is intended to indicate a pressure substantially below atmospheric pressure, and such asis obtained through the use of a vacuum pump or other suitable pressure reducing arrangement.

'I'he invention claimed is:

1. A catalytic ketene, which comprises subjecting acetic acid vapors containing an acetic anhydride-forming catalyst which is gaseous at the reaction temperature, to heating at a temperature between 500 C..900 C., conducting the heating at least under a partial vacuum whereby a mixture containing ketene, water, acetic acid and acetic anhydride is formed and immediately separating at least a part oi' the ketene from the other components.

2. A catalytic process for the production of ketene by the thermal dissociation of acetic acid in the presence of a phosphorus-containing catalyst, which'comprises subjecting acetic acid to tower sprayed with acetic"l process forthe production oftaining catalyst and under at least a partial vacuum, to form ketene as a primary dissociation product, and subjecting at least a part of the ketene to treatment for preventing its recombination into acetic acid and acetic anhydride.- 4

3. A catalytic process for the production of ketene, which comprises heating acetic acid vapors containing a non-metallic, acetic anhydrideforming catalyst under at least a partial vacuum at a temperature between 400 C. and 900 C. to form ketene as a primary dissociation product, and separating water, acetic acid and acetic anhydride from the ketene before it has had time to recombine into acetic` acid and acetic anhydride.

'4. A process for producing ketene, which comprises heating acetic acid vapors under at least a partial vacuum at a temperature greater than 500 C. but less than 900 C. in the presence of anacetic anhydride-forming catalyst, to form ketene as the primary dissociation product, and separating water, acetic acid and acetic anhydride from the ketene.

5. A catalytic process for the production of ketene, which comprises subjecting aceticl acid vapors containing an acetic anhydride-forming catalyst which is gaseous at the reaction temperature, to heating at a temperature between 400 C.900 C.; conducting the heating at least under a partial vacuum whereby a mixture containing ketene, water, acetic acid and acetic anhydride is formed, separating at least a part of the ketene, and reducing the recombination of ,the ketene during separation by carrying out the separation in the presence of a nitrogen-con`` taining'base.

6. A catalytic process for the production of ketene by the thermal dissociatin of acetic acid,

which comprises subjecting acetic acid to heating at a temperature between about 400 C. and 900 C. in the presence of a phosphorus-containing catalyst iand under at least a partial vacuum, to formI ketene as a` primary dissociation product, and subjecting at least a part of the ketene to treatmentv in the presence of a nitrogencontaining base for preventing its recombination into acetic acid and acetic anhydride.

7. A catalytic processv for producing ketene, which comprises subjecting acetic acid vapors to heating under a partial vacuum at a temperature between400 C. and 900 C. in the presence of a non-metallic, acetic anhydride-forming catalyst to form a mixture containing ketene, water, acetic acid and acetic anhydride, and separating the water, acetic acid and acetic anhydride components from the ketene by condensation of said components in the presence of nitrogen-containing compounds. l 8. A process for producing ketene, which com-` l prisesheating acetic acid vapors under at least ketene, which comprises heating-acetic acid vapors containing a volatile ester of phosphoric,

acid, under at least a partial vacuum a a temperature between 400 C. and 900 C., o form ketene as a primary dissociation product and immediately separating water, acetic acid and acetic `anhydride from the ketene.

JOHANN SIXT. MARTIN MUGDAN. 

